Reactive acrylic adhesives are well-known in the art, and are widely utilized due to the numerous advantageous characteristics that they exhibit. Curing of such adhesives may be activated by various chemical initiators, and although compositions are commercially available which react at high rates of speed, increased reactivity will generally be regarded to be advantageous, and will in fact be a fundamental criterion (together of course with appropriate adhesive, chemical and physical properties) for certain applications, such as high-speed, assembly line manufacturing operations.
More particularly, it is known in the art (see for example Bachmann U.S. Pat. No. 4,348,503) that curing of polymerizable acrylate compositions can be effected by use of amine/aldehyde condensation products of the kind that are commercially available from the R. T. Vanderbilt Company, Inc. under the designations VANAX 808 (butyraldehyde/aniline) and VANAX 833 (butyraldehyde/monobutylamine). Bachmann also discloses that ions of iron and other metals can be incorporated into the adhesives thereof, in amounts of 50 to 500 ppm based upon the weight of adhesive, and that it will generally be preferable to introduce the metal in an oxidized valence state.
The same patent indicates the commercial availability of a product, based upon the "833" adduct, which contains a small amount of copper salt, and teaches that the material will not generally be used with the compositions of the patent because of the general preference of incorporating the metal activator in the adhesive formulation. Finally, Bachmann disclosed that, when previously employed for anaerobic acrylate adhesives, ions of iron, copper, manganese, and the like were invariably furnished in admixture with the amine/aldehyde adduct.
Toback et al. U.S. Pat. No. 3,591,438 also teaches the use of the same class of chemical accelerators for curing polymerizable acrylate compositions, either a sulphur-containing free radical accelerator or a compound containing an oxidizable transition metal being incorporated as a reducing activator. According to the patentees, the preferred transition metals are iron, copper, cobalt, nickel and manganese, and they teach that the presence of the transition metal in the lower oxidation state appears to be the essential characteristic, albeit that compounds containing metal atoms which appear in the fully-oxidized state are said to work acceptably in the bonding accelerators of the invention. Toback et al. define the preferred ratio of condensation product:activator to be in the range 0.5-20:1, with little if any benefit being realized otherwise; i.e., they teach the use of about 66.7 to 4.6 percent of the reducing activator, based upon the total mixture. Also, the data set forth in Table Three of the patent appears to indicate that, from the standpoint of achieving the fastest fixture times, the butyraldehyde-butylamine condensation product is more effective than is the butyraldehyde-aniline adduct (compare Sample Nos. 9 and 10).
Despite the activity in the art indicated by the foregoing, a need exists for a reactive acrylate composition which is capable of high-speed curing under both aerobic and anaerobic conditions to produce an adhesive solid having highly advantageous characteristics, utilizing a chemical activator to initiate the curing reaction.
Accordingly, it is the broad object of the present invention to provide a novel, chemically activated, polymerizable acrylate system which is capable of curing under either aerobic or anaerobic conditions, and that cures at high rates of speed to produce a highly effective solid adhesive material.
It is also an object of the invention to provide such a system wherein chemical activation is effected by use of an amine/aldehyde condensation product.
Another object is to provide a novel method for bonding surfaces utilizing such an acrylate system.